In recent years, in order to cope with three-dimensionalization of semiconductor devices, various designs are also required for semiconductor manufacturing processes. For example, as a process of forming a 3DNAND channel, there is a process of forming a silicon (e.g., polysilicon) film constituting a conductive path in a recess having a high aspect ratio and dry-etching the silicon film. As a specific example, there is a process of forming a recess in a silicon oxide layer, forming a monocrystalline silicon layer on the bottom of the recess, covering the inside of the recess with a silicon film, and then removing the silicon film on the bottom by anisotropic etching, which is dry etching, to expose the monocrystalline silicon layer.
After the dry etching, it is necessary to remove a residue generated at the time of the dry etching. For example, in wet etching, if the aspect ratio is high and the cross section of the recess is minute, it is difficult to etch the silicon film in the recess with high uniformity in the depth direction to remove an etching residue. For this reason, the same silicon (e.g., polysilicon) film is stacked on the surface of the silicon film to form a silicon film electrically connected to the monocrystalline silicon layer while leaving the etching residue. In order to improve the conductivity of the silicon film, it is necessary to increase the grain size of the silicon by performing annealing. The grain size grows larger as the film thickness of the silicon film increases. However, when a silicon film is further formed on the surface of the silicon film to which impurities such as an etching residue and the like adhere, the film thickness becomes as small as the interposed impurities, which results in reducing an increase in grain size.
There is also known a dry etching process of silicon using a chlorine (Cl2) gas. However, when the Cl2 gas is used for etching an inner surface of a recess formed in a wafer, the etching amount near the opening of the recess becomes large, so that the inner surface of the recess is etched in a V-like shape. This makes it difficult to assure high uniformity in the depth direction. In addition, when chlorine used as an etching gas adheres to a wall surface and a silicon film is further formed after the etching, the silicon film is etched, which causes a problem in that the film formation rate is reduced or the surface roughness after film formation has deteriorated.